This invention relates generally to a trigger actuated pump dispenser having a pump piston reciprocable within a pump cylinder, the piston having an inboard piston seal and an outboard vent seal. The inner end of the cylinder provides a pump chamber, and the cylinder has in its lower region a vent port positioned outwardly of the pump chamber and in open communication with the interior of the container to which the dispenser is mounted. The vent seal closes communication between the open end of the cylinder and the atmosphere, and the vent seal is positioned outwardly of the vent port in all operative positions of the pump piston. Means at the inner surface of the cylinder permits the passage to by-pass the vent seal from the open end of the cylinder to the vent port during an inward pumping stroke of the piston.
Since the piston seal (sometimes referred to as a power chevron) and the vent seal (or vent chevron) straddle the vent port in all operative positions to the pump piston, the piston when first assembled into the bore must have its piston seal traverse the vent port. During this assembly process the piston seal oftentimes becomes scored as it slides across the inner edge of the vent port. Such damage, even if minor, is known to affect the tight sealability between the piston seal and the wall of the pump cylinder. This break in the seal causes unwanted leakage of product from the pump chamber which is under pressure during the piston power strokes. Such pressurized liquid thus blows by the piston seal and into the annular vent chamber formed between the piston seal and the vent seal. And during the inward pumping stroke of the piston that blow-by fluid escapes from the pump chamber back into the container via the vent chamber and vent port. On the ensuing return stroke, the damaged power chevron will admit unwanted air into the pump chamber via the vent chamber which is briefly opened to atmosphere. This reduces the ability of the pump to suction a sufficient amount of fluid into the pump chamber thus resulting in the pump chamber filled with a mixture of liquid and air. Continued pumping thus results in a poor spray pattern with sputtering of air and liquid through the nozzle orifice.
Also, if the power chevron is damaged during initial assembly, the number of strokes required to prime the pump increase and, depending on the extent of power chevron damage, may not prime at all.
Should damage to the power chevron be small such that the pump can be primed, then output during each piston stroke will be smaller than expected as liquid blows-by the power chevron and returns to the container via the vent chamber and vent port.
The piston seal may be in the form of a chevron seal which curves slightly inwardly at its inner peripheral edge, such that the outer wall surface of the chevron sealingly engages the confronting wall surface of the pump chamber. It is that outer surface which is oftentimes marred during piston assembly into its cylinder bore.
Otherwise the piston seal may be structured as having a sharp edge chevron seal such that the chevron engages the wall of the pump chamber at the outer peripheral edge thereof. This design facilitates a more complete scraping of the wall of the pump chamber during piston reciprocation for maintaining that wall surface completely free of any build-up of any undue film layer or of partly dried condensed particles of product. The pump chevron wipes the pump chamber wall clean during piston reciprocation so as to enhance the sealability between the pump seal and the pump chamber wall at all times.
This latter style pump chevron is even more prone to damage due to interference of its chevron while passing over the vent port during piston assembly. Since the peripheral edge of the chevron seal establishes the tight liquid seal with the pump chamber even minute scoring or marring of the chevron at that peripheral edge could break the tight seal with the pump chamber wall and thereby cause liquid blow-by.